This disclosure is related to three dimensional (3D) image and/or video transforms.
3D subband coding, an extension of 2D subband coding, has recently received increased attention due, at least in part, to the following reasons. First, it typically produces less blocking artifacts, which is a common problem with alternate coding methods, such as motion compensation (MC) and discrete cosine transform (DCT) approaches, particularly at low bitrates. Second, unlike MC compression methods, it does not employ a separate motion estimation stage. Third, it is scalable, both spatially and temporally. The efficiency of the wavelet based codes lies in the applied coding schemes, such as described in an article by Shapiro “Embedded Image Coding Using Zerotrees of Wavelet Coefficients,” IEEE Transactions on Signal Processing, Vol. 41, No. 12, pp. 3445-3459, December 1993, for example, which codes wavelet coefficients efficiently.
Unfortunately, the performance of these techniques may be low when dealing with the wavelet coefficients of low energy content. Furthermore, observation indicates that wavelet coefficients generated by a 3D wavelet transform may be of low energy content. For example, a majority of the wavelet transformed coefficient values may be zero or have a value of small magnitude. The standard method makes several passes to code these frames and, in each of these passes, compares the current threshold value with this low-valued coefficients. This may result in a lower compression ratio and coding efficiency. A need, therefore, exists for an approach that at least roughly maintains coding efficiency and compression ratio.